Eric Voegelin: Philosopher of History, Eugene Webb notes that Voegelin’s thought is not a closed system and it must be seen as a beginning and not an end. Here’s an excerpt from Page 273 in Webb's book:
Because it is not a closed system, Voegelin's thought is not an end but a beginning. As was said, it is an avenue of entry into the study of historical particulars. Much of Voegelin’s own writing has been the beginning of such study, but vast as his historical coverage has been—for a single historian—it remains only a beginning. There are important areas of inquiry he has scarcely touched upon, but which can profit greatly from study in the light of his principles.